In electrical equipment to which a high voltage is applied, for example, in a motor that is used at a high voltage, a high voltage is applied to an insulated electric wire included in the electrical equipment, and partial discharge (corona discharge) is easily generated on a surface of an insulating coating of the insulated electric wire. The generation of corona discharge may cause, for example, a local increase in the temperature, generation of ozone, and generation of ions, which may result in dielectric breakdown at an early stage and result in a decrease in the lifetime of the insulated electric wire, and by extension, the lifetime of the electrical equipment. Therefore, for insulated electric wires used in electrical equipment to which a high voltage is applied, an improvement in the corona inception voltage is also required in addition to a good insulating property, good mechanical strength, and the like.
As as solution for increasing the corona inception voltage, it is effective to realize an insulating coating having a low dielectric constant. There has been proposed an insulated electric wire that includes a heat-cured film (insulating coating) formed by using an insulating varnish containing a coating film-forming resin and a thermally decomposable resin that is decomposed at a temperature lower than a baking temperature of the coating film-forming resin in order to realize an insulating coating having a low dielectric constant (refer to Japanese Unexamined Patent Application Publication No. 2012-224714). In this insulated electric wire, pores are formed in the heat-cured film by utilizing a phenomenon in which the thermally decomposable resin is thermally decomposed during baking of the coating film-forming resin and the resulting decomposed portions become pores. This formation of the pores enables the insulating coating to have a low dielectric constant.